In recent years, an optical communication network enabling large capacity data communication at high speed is expanding. The optical communication network is assumed to be mounted from intra-devices to inter-device in the future. A light guide that can be arrayed is expected to realize the print wiring substrate as an optical wiring.
The light guide has a double structure of a center core, which is called a core, and a capsule, which is called a clad, that covers the core, where the index of refraction of the core is higher than the clad. In other words, the optical signal entered to the core is propagated by repeating total reflection inside the core.
In recent years, in particular, realization of a flexible optical wiring mounted on a smaller and thinner commercially-off-the-shelf device with the light guide is desired. A light guide having high bendability is being developed by using a material more flexible than the related art for the material of the core and the clad of the light guide. The data transmission between the substrates in the device can be carried out with the light guide by using the light guide having high bendability.
A mechanism of light transmission in the light guide module using the light guide will be briefly described. First, a drive portion drives the light emission of the light emitting portion (optical element) based on an externally input electrical signal, and the light emitting portion irradiates the light incident surface of the light guide with light. The light applied to the light incident surface of the light guide is introduced into the light guide (core), propagated by repeating total reflection inside the core, and exit from the light exit surface of the light guide. The light exit from the light exit surface of the light guide is received by a light receiving portion (optical element) and converted to an electrical signal.
The light guide module using such light guide is disclosed in Patent Document 1 to 3, and the like. The conventional light guide modules use an area light emitting laser for the laser emitting portion, and the light incident surface and the light exit surface of the light guide are arranged while inclined with respect to the light transmission direction in a case where the light is transmitted in the core to miniaturize the light guide module. The light from the light emitting portion is applied in the lateral direction with respect to the light transmission direction in the light guide, and the light reflected at the light incident surface is introduced into the core. The light propagated through the core is reflected at the light exit surface and exit in the lateral direction with respect to the light transmission direction.
Patent Document 1: Japanese Laid-Open Patent Publication No. 2000-214351 (date of publication: Aug. 4, 2000)
Patent Document 2: Japanese Laid-Open Patent Publication No. 2000-292656 (date of publication: Oct. 20, 2000)
Patent Document 3: Japanese Laid-Open Patent Publication No. 2005-331535 (date of publication: Dec. 2, 2005)